//  ?:表示对象是否是可选的
function printPoint (point: {x: number, y: number, z?: number}) {
  console.log(point.x)
  console.log(point.y)
  console.log(point.z)
}
printPoint({
  x: 123,
  y: 321
})
printPoint({ x: 123, y: 321, z: 34546})